A thermal-pressure relief device, which has an adapter (20) threaded into the wall of a pressure vessel. The adapter contains an orifice (22) therethrough with a blowout disc (30) overlapping the orifice to obstruct communication with fluid inside the vessel. The disc is attached by brazing with a filler metal in the form of a temperature responsive amalgam (38), preferably a eutectic alloy. When ambient temperatures are elevated above the melting point of the amalgam, the disc is blown out, freeing the orifice, relieving the pressure within the vessel, preventing an explosion. A protective cover in the form of a cap (42) with an impact surface (40) contains the disc when it separates from the adapter and a number of vents (48) diffuse the fluid from the pressure vessel in a safe direction.